Design And Construction Of Spread Spectrum Sequence In Quasi-synchronous CDMA System

The performance of a CDMA system depends to a great extent on the correlation characteristics of spreading sequences,so it is important to choose and design a spreading sequence with good correlation characteristics.The zero correlation zone(ZCZ)complementary sequence has good correlation characteristics within a certain time delay range,not only can meet the quasi-synchronous CDMA system quality requirements,but also can eliminate the multiple access interference in the quasi-synchronous CDMA system.Therefore,constructing the ZCZ periodic complementary sequence set is the focus of this study.This paper first proposes two methods for constructing ZCZ periodic complementary sequence sets.By changing the length of the zero correlation zone,method one improves the construction method of the existing shifted sequences to obtain more different shift sequences.On this basis,a series of ZCZ periodic complementary sequences are constructed by interleaving the complete sequences and several orthogonal columns of matrix partitioned by Hadamard orthogonal matrix,and can be optimized by adjusting the length of the zero correlation zone.The second method interleaves the ZCZ sequence set with the Hadamard orthogonal matrix to obtain a type of ZCZ periodic complementary sequence set that satisfies zero correlation within groups and complementation between groups.This method also expands the length of the zero correlation zone and the number of sequence sets.More users can be supported in a quasi-synchronous CDMA system.Secondly,each row of complementary sequences after shifting the set of periodic complementary sequences is cascaded,and each row of orthogonal matrix is used to expand the concatenated sequence,and a method for constructing a set of mutually orthogonal ZCZ periodic complementary sequences is obtained.This method increases the number of sequence sets,and its orthogonality can satisfy the requirement that neighboring cells do not interfere with each other.Finally,based on the ZCZ periodic complementary sequences constructed above,first of all CDMA and multi-user MIMO are combined to build a MIMO-CDMA system.Then,the ZCZ periodic complementary sequence constructed above is used as a spreading sequence to simulate and analyze the system.Experimental results show that the system using ZCZ periodic complementary sequences has a lower error rate,can effectively eliminate multiple access interference.The construction method of ZCZ periodic complementary sequence set proposed in this paper expands the number of the sequence and the length of zero correlation zone,and provides a new idea for the study of the spreading sequence,which is of great significance.